1. Field of the Invention
The invention relates to a vertical alignment liquid crystal display, and particularly to a vertical alignment liquid crystal display having continuous domains. This application relates to a contemporaneously filed application having the same applicant, the same assignee and the same title therewith.
2. Description of Prior Art
Since liquid crystal displays are thin and light, consume relatively little electrical power and do not cause flickering, they have helped spawn product markets such as for laptop personal computers. In recent years, there has also been great demand for liquid crystal displays to be used as computer monitors and even televisions, both of which are larger than the liquid crystal displays of laptop personal computers. Such large-sized liquid crystal displays in particular require that an even brightness and contrast ratio prevail over the entire display surface, regardless of the observation angle.
Because the conventional TN (twisted nematic) mode liquid crystal display cannot easily satisfy these demands, a variety of improved liquid crystal displays have recently been developed. They include IPS (in-plane switching) mode liquid crystal displays, optical compensation TN mode liquid crystal displays, and MVA (multi-domain vertical alignment) mode liquid crystal displays. In MVA mode liquid crystal displays, each pixel is divided into multiple domains. Liquid crystal molecules of the pixel are vertically aligned when no voltage is applied, and are inclined in different directions according the domains they are in when a voltage is applied. In other words, in each pixel, the effective direction of the electric field in one domain is different from the effective direction of the electric field in a neighboring domain. Typical MVA mode liquid crystal displays have four domains in a pixel, and use protrusions and/or slits to form the domains.
Chinese Pat. Application. No. 01,121,750, published on Jan. 23, 2002, discloses a four-domain MVA liquid crystal display. Referring to FIG. 6 and FIG. 7, the MVA liquid crystal display 1 comprises a first substrate 11, a second substrate 12, a plurality of liquid crystal molecules 16 disposed between the two substrates 11, 12, and protrusions 111, 121 each having a triangular cross-section respectively disposed on the first substrate 11 and the second substrate 12. Components such as first and second polarizers having orthogonal polarization directions, pixel electrodes, common electrodes, thin film transistors and alignment films are also provided in the MVA liquid crystal display 1; however these components are not shown in FIG. 6 or FIG. 7.
FIG. 6 shows the alignment directions of the liquid crystal molecules 16 when the MVA liquid crystal display 1 is in an off state; that is, when no voltage is applied. Most of the liquid crystal molecules 16 are vertically aligned perpendicular to the substrates 11, 12. Accordingly, light beams do not change their polarization states when passing through the liquid crystal molecules 16. Because the polarization directions of the polarizers are orthogonal to each other, light beams that maintain their original polarization states when output from the first polarizer are absorbed by the second polarizer. In other words, the MVA liquid crystal display 1 is in a dark state when no voltage is applied.
FIG. 7 shows the alignment directions of the liquid crystal molecules 16 when the MVA liquid crystal display 1 is in an on state; that is, when a voltage is applied. An electric field perpendicular to the substrates 11, 12 is generated. Because the liquid crystal molecules 16 have negative dielectric anisotropy, they tend to be oriented in directions perpendicular to the electric field. In addition, the protrusions 111, 121 affect the orientations of the liquid crystal molecules 16. For example, the liquid crystal molecules 16 at two opposite sides of the protrusion 111 are respectively oriented from top-right to bottom-left and from top-left to bottom-right. These inclinations change the polarization states of light beams passing through the liquid crystal molecules 16. Therefore a certain amount of light emits from the MVA liquid crystal display 1. In other words, the MVA liquid crystal display 1 is in a lit state when a voltage is applied.
FIG. 8 shows orientation directions of the liquid crystal molecules 16 in four domains A, B, C, D. The protrusions 111, 121 are arranged on the substrates 11, 12 along generally V-shaped paths. Liquid crystal molecules 16 at two opposite sides of the upper portions of the protrusions 111, 121 incline in C and D regions, while liquid crystal molecules 16 at two opposite sides of the lower portions of the protrusions 111, 121 incline in A and B regions. The orientation directions of the liquid crystal molecules 16 in a same inter-protrusion region are consistent. The orientation direction of the liquid crystal molecules 16 in each same inter-protrusion region is orthogonal to the orientation directions of the liquid crystal molecules 16 in all of the other inter-protrusion regions. Therefore, each pixel attains a visual effect that is an overall result of four domains. This gives the MVA liquid crystal display 1 a more even display performance at various different viewing angles.
However, the four-domain configuration can only compensate visual performance in four directions. The overall viewing angle characteristics of the MVA liquid crystal display 1 are still inherently limited, and the MVA liquid crystal display 1 cannot satisfactorily present a uniform display at all viewing angles.
It is desired to provide a vertical alignment mode liquid crystal display which overcomes the above-described problems.